Add the white chocolate and butter to a heatproof bowl. Melt them in a double boiler over a hot water bath or microwave, in 30-second intervals, stirring between each. Set aside to cool for 10 minutes while you prepare the rest ingredients.
Place the pistachios in a food processor and blend to chop and finely chop the dried cranberries.
In a medium-sized bowl, add powdered sugar and sour cream. Mix well until smooth.
Add vanilla extract and mix with a spatula.
Add pistachios, cranberries, and coconut flakes to the sugar and sour cream mixture. Mix gently using a spatula.
Add the melted white chocolate and mix again.
Cover the bowl and refrigerate for 1–2 hours, or until the mixture is firm enough to scoop.
Use a small spoon or melon baller to scoop out portions and roll them into balls with your palms (it helps if your hands are slightly cold).
Roll each truffle in coconut flakes or finely chopped pistachios for a beautiful finish.
Refrigerate for another 30 minutes to firm up before serving.
Notes
Adjust the chilling time: The mixture needs to be firm before you begin scooping, so keep it in the fridge until it is.
Batches: If your house runs on the warmer side, you may want to work in batches as you roll the truffles to prevent the mixture from softening too much.
Make them vegan: You can make the white chocolate pistachio truffles vegan by using coconut cream in place of sour cream, and using vegan butter and vegan white chocolate.